Preparation of high molecular weight polyesters



United States Patent 3,259,607 PREPARATION OF HIGH MOLECULAR WEIGHTPOLYESTERS Harald H. 0. Cherdron, Ittenbach (Rhine), Hans H. Ohse,Oberdollendorf (Rhine), and Friedrich W. A. G. K. Korte, Hangelar uberSiegburg, Germany, assignors to Shell Oil Company, New York, N.Y., acorporation of Delaware No Drawing. Filed Mar. 25, 1963, Ser. No.267,853 Claims priority, application Germany, Mar. 30, 1962,

12 Claims. to. 260-783) The invention relates to a process for thepreparation of polyesters of high molecular weight from lactones and tothe novel polymers produced thereby.

It has been known that lactones polymerize to polyesters of generallyless than ten monomer units, often merely upon standing at roomtemperature. The state of the art in 1932 is excellently summarized, andadditional work reported, by Carothers et al., J.A.C.S. 54, 761 (1932).The authors report, i.a., the conversion of B-valerolactone to waxysolids having molecular weights in the range from 1,000 to 2,500. A fewadditional studies on homopolymerization of lactones have beensporadically reported since that time. The production of lactonehomopolymers of high molecular weights, e.g., of 15,000 and higher,appears to be an unsolved problem to date.

We have now found that, surprisingly, linear crystal? line polyesterpolymers of lactones having 3, 5 or 6 carbon atoms in the lactone ringmay be produced whose molecular weights range from 15,000 to 200,000 ormore. From our findings it appears that the factor which has heretoforeprevented the production of such high molecular weight polylactones isprobably the presence of trace amounts of impurities in the monomer.

According to our invention, high-molecular weight polymers andcopolymers of lactones are obtained in very good yields when highlypurified lactones, specifically those having three and those having atleast five carbon atoms in the ring, are contacted with organic aluminumcompounds which contain at least one alumimum-carbon bond, in thepresence of a controlled small amount of water, sufiicient to act as aco-initiator.

Aluminum compounds suitable for use as initiator include those offormulas AlR AlR X, AlRX Al R X AlR (OR), AlR(OR') and, less preferably,AlR H, wherein each R and R is a saturated hydrocarbyl group, e.g.,alkyl, cycloalkyl, aryl, or hydrocarbon substituted alkyl, cycloalkyl oraryl, preferably of 1 to 12 carbon atoms, and each X is a halogen atom.A single compound may contain diiferent hydrocarbyl groups bound to Al.It is particularly preferred to employ compounds in which X is chlorineand in which each R is an alkyl group. Suitable compounds includealuminum trimethyl, aluminum triisobutyl, aluminum triphenyl, aluminumdiisobutyl chloride, aluminum diethyl bromide and iodide, aluminum ethylsesquichloride, aluminum monoethyl dichloride, aluminum diisopropylmonoisopropoxide and diisobutyl aluminum hydride. Other compounds willbe obvious from the above description. stood that these compounds cannotbe substituted for each other with identical results. For example, ithas been found that use of aluminum compounds having a relatively highratio of halogen to aluminum results in It will be under- I increasedconversion to polymer of lower molecular 3,259,607 Patented July 5, 1966"ice which each R is an ethyl group, and particularly aluminum triethyland aluminum diethyl chloride.

It is advantageous to use the aluminum compound in concentrations from10- to l0 preferably from 10 to l0 mol of initiator per mol of monomericlactone.

The presence of a controlled amount of water as coinitiator is required.It is probable that the initiator is present in the polymerizationmixture as a complex compound with monomers and water, but thisinvention is not to be limited by any hypothesis of its mechanism.

The amount of water used according to the invention is preferably not inexcess of 1 mol per mol of initiator although up to 2 mols may beeffective in some cases. The optimum amount varies from case to case. Inthe polymerization of ,B-propiolactone, for example, it was found thatwith the use of aluminum diethyl monochloride an initiator, between Aand /2 mol, and most suitably about /3 mol of water is employed asco-initiator. With the use of aluminum triethyl as initiator the optimumamount of water as co-initiator is between /5 and 1 mol, most suitably/2 to /3 mol of water per mol of the aluminum compound. With aluminumdiethyl ethoxide, the preferred ratio is about /2 and with aluminummonoethyl dichloride about /6. These ratios are also preferred for usewith other efiective compounds of the type AlR Cl and AlR AlR (OR), andAlRCl respectively, and are generally suitable in polymerizationsaccording to this invention.

The monomers which are polymerized according to this invention arelactones having 3 carbon atoms in the ring and lactones having 5, 6 ormore carbon atoms in the ring, and free of groups or substituentscapable of undergoing polymerization in the presence of aluminumorganiccompounds and water, or if interfering with polymerization through thelactone linkage; e.g., the monomers should be free of olefinic doublebonds. Preferred feeds are fl-propiolactone, 6-valerolactone ande-caprolactone. Mixtures of suitable monomers may be copolymerizedaccording to this invention. It has hitherto not been possible toeffectively polymerize y-bu-tyrolactone according to the process of thisinvention.

It is essential that feeds to the process of this invention be ofextremely high purity, as will be described in more detail below.

The liberation of the lactones from substances which interfere with theionic polymerization, for instance from acid or basic compounds, as wellas from water, may be effected by subjecting the lactone, previouslypurified by fractional distillation, to another fractional distillationtreatment with the addition of suitable substances which bind water asWell as acids or bases, for example, polyphosphoric acid, calciumhydride, or organic isocyanates.

Molecular sieves, ion exchangers, silica gel and the like may be usedfor the purification or partial purification of the lactone. In manycases, two or more purifying treatments are suitably carried out inseries, each with the use of a different agent.

The degree of purity may be checked-by gas-liquid chromatography. Asuitable column packing consists of di-n-decylphthalate, silicone-oil,silicone-grease, or polyethylene glycol as stationary phase, supportedon ground firebrick of .2-.3 mm. particle size. With helium as carriergas and a gas flow of 50 ml./min., at 175 C., retention times are 4minutes for B-propiolactone (B.P. 62" C.); 21 minutes for6-valerolactone (B.P. =107 C.); and 27 minutes for e-CEIPIO- lactone(B.P. =76-78 C.).

It is generally preferred to purify the monomeric lactone to a highdegree, for example as described above, so that it contains less than0.1 mol percent of water, preferably less than 0.01 mol percent, andmost'preferably no measurable amount of water, and thereafter add apredetermined quantity of water to act as coinitiator.

A useful test for monomer purity is the storage stability of themonomer. For example, distilled E-valerolactone was found to beconverted to polymer within a few hours of distillation when stored, noinitiator having been added. Redistillation in the presence ofphenylisocyanate resulted in 6-valerolactone of sufiicient purity foruse in this invention; it did not polymerize spontaneously when stored14 days at 100 C.

In the process according to the invention, polymerization may beelfected in solution, suspension or in bulk. Suitable solvents are, forexample, dioxane, tetrahydrofuran, nitrobenzene, and glycol dimethylether. Aromatics, e.g., toluene, are suitable for lactones having ormore carbon atoms in the lactone ring. A 10-20% solution of a lactone inone of said solvents is a suitable polymerization feed, but any otherconcentrations may also be used in the process according to theinvention. It is also possible to employ suspension polymerization,e.g., in n-hexane.

The solvents or diluents require careful drying and purification; thesame methods may be employed as in purifying the monomers. Thpolymerization vessels should be thoroughly clean and dry. It isgenerally advantageous to exclude oxygen.

The polymerization reactions of this invention may be carried outeffectively over a broad range of conditions. Reaction temperatures mayrange from room temperature to 100 C. and times from 1 hour or less tomore than 50 hours, the shorter times being employed at the highertemperatures. Times from 12 to 50 hours or more may be used at roomtemperature. Subatmospheric and superatmospheric pressures may beemployed.

The high-molecular Weight polymers obtained by the process according tothe invention are solid, crystalline polyesters, with melting pointsgenerally in the range from 50 to 100 C. They may be used as lacquer rawmaterials, worked up to films or fibers, or may be used as components inpolymer mixtures to impart desirable properties.

According to the process of the invention polymers can be obtainedhaving a number average molecular weight above 15,000, in many instancesabove 20,000 and in some instances up to 200,000. Although measurementusually is expressed in terms of intrinsic viscosity (dl./g.), it ispossible in the case of fi-valerolacton to calculate the molecularweights by a calibration curve which is based on end-groupdetermination. An intrinsic viscosity of 0.2 dl./ g. (determined inbenzene at C.) is found to correspond to a molecular weight of about20,000.

Typical poly(fi-propiolactones) are substantially linear polymers inwhich the repeating unit is They melt at 70100 C., are solubl inchloroform and formic acid and generally in methylene chloride, dioxane,dimethylsulfoxide, and glacial acetic acid, and are insoluble in diethylether.

Typical poly(6-valerolactones) are substantially linear polymers inwhich the repeating unit is They melt at 50-60 C., are soluble inaromatic hydrocarbons, e.g., benzene and toluene, as well as in solventsfor poly-,B-propiolactones, and are insoluble in diethyl ether.

Typical poly(e-caprolactones) are substantially linear polymers in whichthe repeating unit is 0 -[OCH:CHz--GH2CHz-CH2%:| Their melting pointsand solubilities are like those of poly( a-valerolactones) In theiroriginal state, all these polymers are white, flocky or fibrous,odorless materials, generally having number average molecular Weightsabove 15,000. X-ray diffraction patterns show them to be crystalline.They appear to contain one hydroxyl end group and one carboxyl end groupper polymer molecule.

1 The infrared absorption spectra of fi-valerolactone polymers of thisinvention are characterized by a sharp absorption band at 1320 cm- Theprocess will be further illustrated by the following examples.

EXAMPLE 1 fl-propiolactone which had been subjected to simple distillation was redistilled at 20 mm. pressure with the addition of 2% byWeight of toluene diisocyanate (TDI) in a 1.5 m. high, automaticallycontrolled column, packed with Raschig rings. The lactone was takenoverhead; TDI remained as bottoms. The fraction with a boiling point of62 C. (20 mm.) and a refractive index n =1.4478 was collected and testedfor purity by gas chromatography. With a column packing of siliconegrease on firebrick, a temperature of 200 C. and helium as carrier gasthe column only showed one peak of fi-propiolactone. (Water content:0.00 mol percent) 5 ml. of the said pure fi-propiolactone was placed ina 50 ml. one-necked flask equipped with a side arm for the vacuum and/ornitrogen tube which flask had been preheated in vacuo, after which firstthe amount of water mentioned in Table 1 below and subsequently aquantity of 1X10 mol of aluminum diethyl monochloride per mol of lactonewere added by means of an injection syringe. Polymerization temperature:50 C.; polymerization: 72 hours. After the desired time period hadelapsed, the polymer solution was dropped into 6-8 volumes of ether andthe precipitated flocky to fibrous white polymer collected on a glassfrit, washed with ether, and dried in vacuo over calcium chloride.

The conversion and the intrinsic viscosity [1;] (measured in chloroform)of the polymers obtained are given in Table 1:

Table 1 Water Conversion, [17] Experiment No. Percent Pcrcentby Mol/molof wt. initiator 1 Based on lactone.

Maxima of conversion and molecular weight of polymer were found at aboutthe same ratio of water to initiator when difierent reactiontemperatures in the range from 20 C. to 60 C. were employed.

EXAMPLE 2 o-valerolactone which had been subjected to simpledistillation was fractionally redistilled at reduced pressure in thecolumn described in Example 1, with 5% by weight of phenylisocyanate(PI). The PI distilled first and was recovered. The fraction with aboiling point of 107 C. (10 mm.) and a refractive index of n =1.4530 wascollected and tested by gas chromatography in a manner similar to thatdescribed in Example 1. in ad- 5 6 dition to a pealr attributable to thefi-valerolactone, a Table 4 small second peak was found. Distillationwas therefore repeated with the addition of 3% by weight of cal-ReducedViscosity cium hydride. Gas chromatography showed the redis- (ing g g g tilled product to be pure. As described in Example 1, 5 theamounts of water mentioned in the table and 1X 10- 75 80 18 mol ofaluminum triethyl per mol of lactone were added 7H0 to 5 m1. of thispure B-valerolactone. Polymerization ga 13 time: 21 hours;polymerization temperature: 50 C. The 7) 1 conversion and 01 (measuredin benzene) are given in 10 Table EXAMPLE 5 Similarly, polymers ofa-valerolactone were prepared Table 2 and found to have the propertiesshown in Table 5.

Table 5 Water Experiment Conversion [-1 M11 M.P., C. M-11 PercentMoi/mol of percent by wt. initiator 5e 7 70,000 0 00.7 0.32 38,000 mtdetermined 0.035 0.14 61.0 0.32 38,000 27'000 0.087 0. 35 62.5 0. 3552,000 65000 0.120 0.49 00.1 0.44 100, 000 0.175 0.70 75.0 0.42 83,0000. 220 0. 84 72.0 0. 40 75,000 0.260 1.11 57.5 0.37 58, 000 EXAMPLE .70. 350 1. 39 0 A copolymer of fl-propiolactone and e-valerolaotone, 1Based 0n1act0ne polymerized in a volume ratio of 7:3, was found to meltat 65-8S C.

EXAMPLE 8 EXAMPLE 3 30 A polymer of e-caprolactone was found to have amelte-caprolactone, which had been subjected to simple ing point of 5657C. and a molecular weight of 20,000. distillation was fractionallyredistilled in a column as in Example 1, with the addition of 3% ofphenylisocyanate. EXAMPLE 9 As in Example 2, it was found thatpurification was still A ehloroform Solution of high molecular Weightpols incomplete, and the lactone was re-fractionated with the (avalerolaetohe) Similar to these of Example 2 was addition of 2% ofpolyphosphoric acid. The product col- Poured onto a glass plate Uponevaporation of the lecled at 762780 (0-02 mercury) had a minechloroform, a thin, tough film of polymer was found to tive index of Dand was found F pure, by have been formed. Similar films can be formedfrom gas'chmmatograplly Example It 15 Sultably 40 polymers of Examples 1and 3. The films may also be lymel'ized as descnbed Example Even Shorterformed on other substrates and can serve as decorative tiou times, e.g.,3 hours, are effective, and polymers are and protective coatings. ofespecially high molecular weight, generally between 100,000 and 200,000.EXAMPLE 10 EXAMPLE 4 A chloroform solution of poly(6-valerolactone), asin Example 9, was extruded through a nozzle into methanol,Polymerlzatlqns were 'i the manner of E resulting in the production offibers. Fibers can be simiample l, but with a reaction time of 21 hours,and w th formed from the Polymers of Examples 1 and several differentaluminum compounds. The following We claim as ourihvehtion; data, inTable 3, reflect the conditions at which percent 1 A process for theproduction of highhloleeular conversion and molecular weight,respectively, reached weight polylactohes comprising polymerizing alaetohe Observed maxlmaselected from the group consisting ofbeta-propiolactone,

delta-valerolactone, and epsilon-caprolactone by maintaining it incontact at a temperature in the range from Table 3 room temperature to100 C. with 10* to 10 mole per mole of said lactone of a catalystconsisting of an organo- Water aluminum compound selected from the groupconsisting Experiment Converof aluminum trialkyls and aluminum alkylalkoxides A1 Compound Moi/m of ,223,, "1 wherein the alkyl groups havefrom 1 to 12 carbon atoms, initiator together with a carefullycontrolled, catalyst-modifying amount of water in the range from /5 to 1mol per mol 0.68 18.0 0. of aluminum compound. 8'23 232 8-11 2. Aprocess for the production of high-molecular 0:14 3211 0118 weightpo-lylactones comprising polymerizing a lactone AlEtCl 1L2 65 selectedfrom the group consisting of beta-propiolactone,

delta-valerolactone, and epsilon-caprolactone by maintaining it incontact at a temperature in the range from room temperature to C. withfrom 10 to 10- Wlth 2( mol Hzo/mol A1 P P Sun mole per mole of saidlaotone of a catalyst consisting of resulted 1n a significant amount ofpolymerizatlon. 7 an orgaho a1umihum eompeuhd selected from the groupconsisting of aluminum alkyl halides wherein the alkyl EXAMPLE 5 groupshave from 1 to 12 carbon atoms, together with a Novel high molecularweight polymers of B-propiocarefully controlled, catalyst-modifyingamount of water lactone were prepared by various different methods andin the range from Ms to /2 mol per mol of aluminum found to have theproperties shown in Table 4. 7 compound.

3. A process according to claim 1 wherein said lactone isbeta-propiolactone of high purity, characterized by a refractive indexof n =L4478 and a gas-liquid chromatogram showing no contaminatingimpurities.

4. .A process according to claim 2 wherein said lactone isbeta-propiolactone of high purity, characterized by a refractive indexof n =1.4478 and a gas-liquid chromatogram showing no contaminatingimpurities.

5. A process according to claim 1, wherein said lactone isdelta-valerolactone of high purity, characterized by a refractive indexof n =1.4530 and a gas-1iquid chromatogram showing no contaminatingimpurities.

6. A process according to claim 2 wherein said lactone isdelta-valerolactone of high purity, characterized by a refractive indexof n =1.4530 and a gas-liquid chrmatogram showing no contaminatingimpurities.

7. A process according to claim 1, wherein said lactone isepsilon-caprolactone of high purity, characterized by a refractive indexof n =L4621 and a gas-liquid chromatogram showing no contaminatingimpurities.

8. A process according to claim 2 wherein said lactone isepsilon-caprolactone of high purity, characterized by a refractive indexof n =1.4621 and a gas-liquid chromatogram showing no contaminatingimpurities.

9. A process according to claim 3 wherein said organoaluminum compoundis aluminum triethyl and said '8 amount of water is in the range from /2to mol per mol of aluminum triethyl.

10'. A process according to claim 3, wherein said organo-aluminumcompound is aluminum diethyl ethoxide and said amount of water is in therange from A: to mol per mol of aluminum diethyl ethoxide.

11. A process according to claim 4, wherein said organo-alurninumcompound is aluminum diethyl chloride and said amount of water is in therange from A5 to /2 mol per mol of aluminum diethyl chloride.

12. A process according to claim 4, wherein said organo-aluminumcompound is aluminum ethyl dichloride .and said amount of water is inthe range from /5 to /2 mol per mol of aluminum ethyl dichloride.

References Cited by the Examiner UNITED STATES PATENTS 3,021,310 2/1962Cox et a1. 26078.3 3,021,313 2/1962 Cox et a1. 26078.3 3,111,469 11/1963Marans 260-783 3,190,858 6/1965 COX et a1. 260-783 JOSEPH L. SCHOF-ER,Primary Examiner.

L. WOLF, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF HIGH-MOLECULAR WEIGHT POLYACTONESCOMPRISING POLYMERIZING A LACTONE SELECTED FROM THE GROUP CONSISTING OFBETA-PROPIOLACTONE, DELTA-VALEROLACTONE, AND EPSILON-CAPROLACTONE BYMAINTAINING IT IN CONTACT AT A TEMPERATURE IN THE RANGE FROM ROOMTEMPERATURE TO 100*C. WITH 10-1 TO 10-6 MOLE PER MOLE OF SAID LACTONE OFA CATALYST CONSISTING OF AN ORGANOALUMINUM COMPOUND SELECTED FROM THEGROUP CONSISTING OF ALUMINUM TRIALKYLS AND ALUMINUM ALKYL ALKOXIDES,WHEREIN THE ALKYL GROUPS HAVE FROM 1 TO 12 CARBON ATOMS, TOGETHER WITH ACAREFULLY CONTROLLED CATALYST-MODIFYING AMOUNT OF WATER IN THE RANGEFROM 1/6 TO 1 MOL PER MOL OF ALUMINUM COMPOUND.
 2. A PROCESS FOR THEPRODUCTION OF HIGH-MOLECULAR WEIGHT POLYLACTONES COMPRISING POLYMERIZINGA LACTONE SELECTED FROM THE GROUP CONSISTING OF BETA-PROPIOLACTONEDELTA-VALEROLACTONE AND EPSILON-CAPROCTONE BY MAINTAINING IT IN CONTACYAT A TEMPERATURE IN THE RANGE FROM ROOM TEMPERATURE TO 100*C. WITH FROM10-1 TO 10-6 MOLE PER MOLE OF SAID LACTONE OF A CATALYST CONSISTING OFAN ORGANO-ALUMIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALUMIUMALKYL HALIDES WHEREIN THE ALKYL GROUPS HAVE FROM 1 TO 12 CARBON ATOMS,TOGETHER WITH A CAREFULLY CONTROLLED, CATALYST-MODIFYING AMOUNT OF WATERIN THE RANGE FROM 1/6 MOL PER MOL OF ALUMINUM COMPOUND